1. Field of the Invention
The present invention relates to semiconductor processing in general, and particularly, to a novel apparatus for in-situ detection of ions in an ion implant beam during wafer processing.
2. Description of the Prior Art
FIG. 1 is a schematic diagram depicting an ion beam implantation device 10, such as an Axcelis GSD-200 Beam Line (Axcelis Technologies, Beverly Mass.), which is a low energy and high current implanter for high-speed wafer handling in advanced ion implant manufacturing processes.
The ion beam implantation device includes an ion source 12 including a gas delivery system for producing an ion beam 15. The ion beam passes through a pre acceleration section, known as the source extraction 18. During ion implantation, the ions extracted from the source contain many kinds of ions, and ionized compounds, that are either of a species desired for implantation, or not. A mass spectrometer unit (or mass analyzing magnet) 20 positioned along the beam path between the source and a process chamber 25 filters ions from the beam while allowing ions of the desired species to exit aperture slits 28 provided in the implanter""s post acceleration assembly 30 and enter the process chamber. The magnet 21 includes multiple magnet pole pieces constructed from a ferromagnetic material and having inwardly facing pole surfaces. Particularly, to sort the desired ions from the supply of ions, the ions are accelerated through a series of magnets, an analyzer magnet, where the magnetic fields are set so that the ions of an ion beam 15 of the desired species are deflected in a deflection region 36, make a turn, and travel through the aperture slits 28 for implantation onto the wafers. The relationship between the magnetic field (B), the ion accelerating voltage (V), the mass-to-charge ratio (m/q in atomic mass units per proton charge), and the radius of ion curvature (r) in the magnetic field, i.e., m/q=(B2/2V)r2, is well known to skilled artisans. The magnetic fields of the mass spectrometer 20 are thus adjusted so that the interaction with ions of the desired species to be implanted (i.e., having ions of desired mass/charge ratio and velocity) are deflected in a manner so that they exit the mass spectrometer device 20 and ion implanter 10 for implantation in a wafer (not shown). That is, the resulting desired ion beam species 15a is caused to pass through an aperture slit 28 for implantation in the process chamber 25. With respect to undesirable ions, ion compounds and contaminants, e.g., ions 16a, 16b in FIG. 1, these ions interact with the magnetic field in a manner such that they are deflected and collide with the graphite walls 22a, 22b of the mass spectrometer unit 20. Such undesirable ions comprise contaminants which may be passed with the desired ions, such as BF2, or other implanted species. With respect to the ion beam that passes through the mass spectrometer, as shown in FIG. 1, a Faraday cup 38 is arranged in the process chamber 25 and beam line 15a, corresponding to an ion beam shooting position. The Faraday cup device 38 is implemented for measuring the current of the ion beam of the desired species, without significant affecting the flow of ions to the wafer.
A way of determining the other ions being extracted from the source is to ramp the magnet current of the analyzer magnet (where the magnet current to ion/mass relationship is known) and measure the resulting ion beam current, stating the presence, and quantity of certain ion masses. The problem is that this technique takes time away from the manufacturing operation of the tool, and can only be measured while the ion beam is not implanting the wafers (i.e., off-line).
Thus, it is the case that ion beam spectrums may currently be performed, which is a time consuming process, and cannot be done while the wafers are actually being implanted with desired ions. Another technique is to connect an RGA (Residual Gas Analyzer) to the chamberxc3xa2∈¦ but this has the disadvantage of measuring only certain materials, and not ionized ones, and not ionized compounds.
It would be highly advantageous to provide a ion implanter in situ mass spectrometer that would allow the components of the ion beam to be measured continuously, even while the wafer is being implanted.
It is an object of the present invention to provide an apparatus for detecting ions in an ion implant beam in real time during wafer processing.
The invention consists of imbedding a strip of current detectors into the graphite shields along the walls of the analyzer magnet channel, connected by a multi-channel detector. This would allow continuous monitoring of the beam current (and quantity) of ion beam contaminants.
Thus, according to a first aspect of the invention, there is provided an apparatus for the in-situ detection of ions in an ion beam implanter beam includes a mass spectrometer device having inner and outer walls and, a system for generating and directing an ion implant beam through the mass spectrometer device. The in-situ mass spectrometer device generates a magnetic field for directing ions of the ion implant beam of a desirable type through an aperture for implanting into a semiconductor wafer, and causing ions of undesirable type to collide with the inner or outer wall. A detector device is disposed on the inner and outer walls for detecting the second type of ions deflected.
According to a further aspect of the invention, there is provided a mass spectrometer device for the in-situ detection of ions, the device comprising:
an inner wall, an outer wall and an aperture defining an area through which an ion implant beam is directed for implanting into a semiconductor wafer;
means for generating a magnetic field for interacting with the ions of the implant beam, the ions comprising ions of a desirable type to be directed through the aperture, and ions of undesirable type, the magnetic field interacting with the undesirable type ions to collide with the inner or outer walls; and, a detector device disposed on the inner and outer walls for detecting the ions of the undesirable type.
In one embodiment, the detector device comprises electronic sensor devices for detecting a concentration of the second or undesirable type ions. In another embodiment, the detector device comprises Faraday cup devices for detecting a concentration of ions of the second or undesirable type ions, or, may comprise a Faraday device positioned along tracks disposed respectively along the inner and outer wall, the Faraday being driven for reciprocal movement along a respective track. Data is collected from the sensors corresponding to the positions of undesirable ion detected and is processed, in real-time, during wafer processing. In this manner, potential contaminants in the ion implant beam may be determined and corrective action may be taken in response.